Devices and systems employing fiber optics typically include a number of optical components that must be interconnected to form an optical path for the transmission of data. In one approach, optical components are mounted onto a printed circuit motherboard, and their optical fiber leads are then spliced together. The splicing process, however, is complicated by the relative fragility of optical fiber, which can be damaged by bending, excessive tension, or other stresses. Excessive signal attenuation due to bending of the fiber is also an issue. Further, the splicing process may require more than one attempt, if it is determined that the splice was not successfully made. In such a case, the improper splice must be broken out, the leads trimmed back, and a new splice performed. Finally, the continuous loop of fiber that results from a splice must be properly stowed away to prevent damage to the fiber.
FIG. 1 is a perspective view of one approach for mounting an optical component 10 onto a motherboard. The optical component 10 includes optical fiber leads 12, extending from either end. A cable tie 14, or spring clip, is used to attach the optical component 10 to a holder 16, which is fabricated from a glass-filled polymer or other suitable material that has coefficient of thermal expansion is close to that of optical fiber, is moldable and machinable yet stiff, and has other useful properties. Finally, the holder 16 is affixed to a motherboard by means of a pair of plastic rivets 18. This process is performed for all of the optical components used in the device being manufactured. Once all of the optical components have been securely mounted to the motherboard, their fiber leads must then be spliced together to create an optical path for the transmission of data. However, the task of splicing optical fiber leads together is far more complex than the splicing of electrical component leads.
The splicing task is typically a precise one. If the cores of two spliced fiber leads are not properly aligned, the optical path may be interrupted. In that event, the improper splice must be broken out and another splice performed. Thus, optical fiber leads tend to be quite long compared to electrical component leads, in order to provide a worker with an adequate amount of fiber to make numerous attempts at a proper splice.
However, this in turn means that the splicing together of two optical component leads results in a continuous loop of fiber, the length of which depends upon the amount of fiber required to achieve a proper splice. Because optical fiber is easily damaged, it is generally undesirable to have long loops of fiber freely floating within an optical device. Rather, the loops of fiber resulting from splices must be stowed away in a manner that will not result in damage to the fiber arising from bending, tension, or other mechanical stresses.
FIG. 2 is a partial perspective view of a system for managing the continuous loops of optical fiber resulting from the splicing of optical leads. The system provides a matrix of curved guides 20, 22a-d, made from a glass filled polymer or another suitable material, that are mounted to a motherboard 24. As described below, loops of optical fiber resulting from splices are protected from damage by winding them around the curved guides in a predetermined pattern. The length of these loops is precisely measured using grids 28a and 28b so that an optimal level of slack is maintained in the loops after they are wound over the curved guides, the tension in the loops being sufficient to hold them in place on the guides without causing damage to the fiber or degrading the optical characteristics of the fiber.
The matrix of curved guides includes a set of six central coil guides 20 that are arranged to form a central coil. These central coil guides 20 are shaped, and are positioned relative to each other, such that optical fiber can be wound around them without causing damage to the fiber. In addition, the matrix of curved guides includes pairs of auxiliary guides 22a-b, 22c-d that are mounted onto the motherboard 24 on either side of each optical component, 10a, 10b. Each of these pairs of auxiliary curved guides 22a-b, 22c-d is shaped, and positioned relative to the central coil and to the optical components, such that the auxiliary curved guides 22a-b, 22c-d provide safe winding paths for the optical fiber leads 12 from their respective optical components to 10a, 10b the central coil.
The functions of the central coil guides 20 can better be understood with reference to a specific example. FIG. 2 shows first and second optical components 10a, 10b, which are mounted to the motherboard 24. (For clarity of illustration, only one holder 16a is shown, although in an actual device, each optical component is held by its own holder). Each of these two optical components 10a, 10b has a pair of optical fiber leads 12a-b, 12c-d, extending from either end. In this example, a first lead 12a, that extends from the left end of the first optical component 10a, is spliced to a second lead 12d, that extends from the right end of the second optical component 10b.
Prior to the actual splicing of the two leads together, each lead must first be precisely measured and then trimmed, so that the continuous loop of fiber resulting from the splice will be the correct length. Measuring grids 28a, 28b are provided on the motherboard 24 to allow the worker to precisely determine the point at which the two leads 12a, 12d are to be spliced. Of course, the point chosen for the splice 30 must provide clearance for a splicing sleeve 26 between the center coil guides 20. Once a splicing point has been determined, using a measuring grid, the first lead 12a and the second lead 12d are marked for length along the measuring grid.
The leads 12a, 12d are then stripped, cleaned, and cleaved at the marked splicing point so that the leads will meet at the proper spot and the splicing sleeve 26 is on a straight run. If that operation is successfully accomplished, the splicing sleeve 26 is then acrylated in place over the splice 30, forming a long, continuous loop of fiber 32 extending from the left end of the first component 10a to the right end of the second component 10b. If the splice 30 has been properly measured and executed, the length of the continuous loop of 32 is such that it will just fit over the center coil guides 20, with the splicing sleeve 26 coming to rest in its predetermined position.
The motherboard includes rows of optical components 10, with leads 12 extending out of either end. Because the position of each optical component is fixed, and because the splicing point for each pair of leads must be carefully measured and executed within a narrow tolerance, this method of splicing optical fiber leads is called a "deterministic" fiber wrapping process. As the complexity and quantity of optical communication systems modules increases, a number of disadvantages of the deterministic process have become apparent.
First, the above-described method for wrapping fiber requires a high degree of skill on the part of the worker performing the splicing process. The process of splicing optical fiber is a difficult, painstaking task, which is complicated by trying to achieve sufficient slack in the fiber after it is wrapped back onto the center coil guides. If the fiber is too tight, light loss may occur, and the fiber may even snap. If the fiber is too loose, the fiber may slide up and off the guides and wander within the device, which can cause it to get pinched or otherwise damaged by other components.
Second, the above-described method requires the use of a stiff platform to manufacture an assembly having mostly optical components and relatively few electronic components. Passive platforms can be manufactured from less expensive materials, resulting in greater cost efficiency.
Third, the loading of a platform with rigid guides and holders is a lengthy, time consuming process.
Finally, it is inefficient to go through the arduous loading, splicing and wrapping procedure, only to learn at a final test that a component loaded at the very beginning is inoperable and must be replaced.
These and other issues are addressed by the invention described herein. Optical components are loaded into a specially designed passive platform module that is preferably constructed out of foam, elastomer, or other compliant material. In a first embodiment of the present invention, the platform is constructed from a fairly dense foam material, exemplary of which is a foam having a density of approximately four-pounds per cubic foot. Foam is a very inexpensive material. Even fabricated, its cost is far less than that of the use of rigid guides and holders on a printed circuit board, as described above. Foam will not harm optical fiber, even if the foam is rough in texture.
At present, in order to address these concerns, a so-called "deterministic" system can be used, in which the position of the optical component is fixed, e.g., by mounting it firmly in place on a motherboard, requiring the splice be made at a precise location at the ends of the mating fiber leads. As described below, this system has a number of disadvantages, both because of cost, and high degree of the skill required to execute the splice in the proper position. These and other disadvantages are addressed by the present invention.